An X-ray C-arm system is X-ray imaging apparatus that is used by healthcare professionals to obtain real-time images of internal structures of a patient, such as the vasculature. The imaging apparatus may be a rotational X-ray imaging device that acquires a series of 2D X-ray projections of the anatomical region of interest along an arced path. The type and configuration of the imaging apparatus varies but generally the rotation is accomplished by moving an X-ray source and an X-ray detector, mounted on respective ends of a rotatable C-shaped gantry, about a patient. The X-ray detector converts the raw X-ray projections into image data signals for subsequent image processing by the X-ray imaging system.
X-ray C-arm systems are routinely used in medicine during interventional medical procedures to acquire images for various reasons, for example: a) diagnostic examination of a patient's vascular structures, b) guidance of interventional therapeutic procedures such as stent placement, coiling of aneurysms, and embolization of arteriovenous malformations (AVMs), c) assessment of the efficacy of an interventional therapeutic procedure, and d) assessment of disease progression.
To diagnose, treat, and follow-up on vascular diseases, healthcare practitioners like radiologists use 2D and 3D angiography images to understand the structure and interconnections of a patient's vascular anatomy and the dynamic blood flow properties of the vasculature. 2D angiograms are X-ray projection images of vascular structures filled with contrast agent, which has been injected through a catheter. 3D angiograms can be obtained by rotating the X-ray C-arm around the patient, acquiring a set of angiograms as 2D projection images during the rotational run, and then reconstructing a 3D volume image from these set of projections. Digital subtraction angiography (DSA) is one of several techniques that can then be used to separate the imaged blood vessels from the surrounding anatomy. DSA specifically subtracts two X-ray images, one with and one without contrast injection. The background anatomy cancels out, and the contrasted vessel is highlighted.
Repeated acquisition of angiographic images for the same anatomical region is often necessary for treatment, and for follow-up procedures. For example, during an interventional medical procedure, it is usually important to compare the vessel anatomy and blood flow pattern before and after the insertion of a device, such as a coil or a stent, inside the patient's artery. Also, at the end of an interventional medical procedure, an angiographic image of the overall anatomical organ treated (e.g., left cerebral hemisphere) is required in order to compare the blood vessel anatomy and flow dynamics before and after the treatment. Also, repeated acquisition of angiographic images permits a comparison of the blood vessel morphology and blood flow pattern during a follow-up to a procedure or treatment in order to assess disease progression.
However, the generation of a 2D angiographic image that matches or closely matches another acquired at a previous time for these comparisons is often challenging. This is because slight variations in patient positioning on the radiographic table, differences in table height, translation, zoom setting, and C-arm angles may produce significantly different images. Using the state-of-the-art angiographic C-arm systems, the healthcare practitioner has to continuously apply X-ray fluoroscopy, while intermittently injecting angiographic contrast, in order to adjust the C-arm and table positions so that the resulting image visually matches a 2D angiographic image acquired at a previous time point. This subjects the patient to an additional dosage of X-rays, an additional dosage of contrast, and lengthens the procedure time. Since this approach depends on visual comparisons and manually-driven movements of components of the C-arm system, it is tedious and it often fails to produce a 2D image that accurately matches another acquired at a previous time point. Secondly, the patient's position on the radiographic table may be different between the initial angiogram and the second angiogram due to the acquisition of the two images on different days, or due to a patient's motion in between the two imaging times. The trouble in producing a 2D image that accurately matches a previously-acquired image may lead to the difficulty in assessing disease progression or the efficacy of treatment, since the two images being compared do not lend themselves to a point-to-point comparison.
Consequently, there is a need to overcome the limitations of state-of-the-art angiographic C-arm systems in allowing easy and fast acquisition of a 2D angiographic C-arm image that matches or substantially matches another image of the same anatomical region acquired at a previous time point. Further, there is a need of a method that allows straight forward comparison between two images of the same anatomical region generated at different times.